A fuel cell, for example, a polymer electrolyte fuel cell, is an apparatus in which a fuel gas containing hydrogen and an oxidant gas containing oxygen, such as air, are electrochemically reacted with each other in a gas diffusion layer having a catalyst layer made of platinum or the like so as to simultaneously generate power and heat.
FIG. 30 is a cross-sectional view that schematically shows a basic structure of a conventional polymer electrolyte fuel cell. A single cell (referred to also as a “cell”) 100 of the polymer electrolyte fuel cell is provided with a membrane electrode assembly 110 (hereinafter, referred to also as an MEA: Membrane-Electrode-Assembly) and a pair of plate-shaped conductive separators 120 and 120 that are disposed on two surfaces of the MEA 110.
The MEA 110 is provided with a polymer electrolyte membrane (ion exchange resin membrane) 111 that selectively transports hydrogen ions, and a pair of electrode layers 112 formed on the two surfaces of the polymer electrolyte membrane 111. The pair of electrode layers 112 are formed on the two surfaces of the polymer electrolyte membrane 111, and each of these has a catalyst layer 113 mainly comprised of carbon powder on which a platinum catalyst has been supported, and a gas diffusion layer 114 (also referred to as a GDL) that is formed on the catalyst layer 113 and compatibly has a current-collecting function, gas permeability, and water repellency. The gas diffusion layer 114 is comprised of a base material 115 made from carbon fibers, and a coating layer (water-repellent carbon layer) 116 comprised of carbon and a water repelling member.
On a main surface of each of the pair of separators 120 and 120 that is made in contact with the gas diffusion layer 114, a gas flow passage 121 with a rectangular cross-sectional shape that allows a fuel gas or an oxidant gas serving as a reaction gas to flow therethrough is formed. A gas flow passage 121 formed on one of the separators 120 serves as a fuel gas flow passage used for flowing a fuel gas, and another gas flow passage 121 formed on the other separator is an oxidant gas flow passage used for flowing an oxidant gas. On mutually adjacent surfaces of the pair of separators 120 and 120, a cooling-water passage 122 through which cooling water or the like is allowed to pass is formed. A fuel gas is supplied to one of the electrode layers 112 through the one of the gas flow passages 121, and an oxidant gas is supplied to the other electrode layer 112 through the other gas flow passage 121 so that an electrochemical reaction occurs to generate power and heat.
As shown in FIG. 30, two or more of the cells 100 constructed as described above are generally stacked and used, with the adjacent cells 100 being electrically connected in series with each other. At this time, the mutually stacked cells 100 are pressurized and fastened with each other under a predetermined fastening pressure applied by fastening members 130 such as bolts, so as to prevent a reaction gas from leaking, and also to reduce contact resistance. Therefore, the MEA 110 and the separator 120 are made in face-to-face contact with each other by a predetermined pressure. At this time, the separator 120 exerts a current-collecting function so as to electrically connect the mutually adjacent MEAs 110 and 110 in series with each other. Moreover, in order to prevent a gas required for an electrochemical reaction from externally leaking, a sealing member (gasket) 117 is disposed between the pair of separators 120 and 120 so as to cover the side faces of the catalyst layer 113 and the gas diffusion layer 114.
In recent years, in the field of fuel cells, there have been strong demands for lower costs, and from the viewpoints of reduction of unit costs of the respective components and reduction of the number of parts, various techniques for cutting costs have been proposed. One of these techniques includes a technique in which gas flow passages 121 are formed not in the separator 120, but in the gas diffusion layer 114.
In the conventional fuel cell shown in FIG. 30, gas flow passages 121 are formed in the separator 120. As a method for achieving this structure, an injection molding method is proposed in which, for example, carbon and a resin are used as materials for the separator 120, and by using a metal mold having convex portions, each having a rectangular cross-sectional shape corresponding to the shape of the gas flow passage 121, these materials are injection-molded. However, this method has an issue of high production costs. Moreover, as another method for achieving the above-mentioned structure, metal is used as a material for the separator 120, and by using a metal mold having concave portions each having a rectangular cross-sectional shape corresponding to the shape of the gas flow passage 121, the metal is rolled. However, although this method achieves lower costs in comparison with the injection molding method, the separator 120 is easily corroded, resulting in an issue in that power generation performances as the fuel cell are lowered.
In order to provide a gas diffusing property, the gas diffusion layer 114 is comprised of a porous material. For this reason, it is easier to form a gas flow passage 121 in the gas diffusion layer 114 than to form the gas flow passage in a separator, and this arrangement is more advantageous in reducing costs and achieving high power generation performances. The gas diffusion layer having such a structure is, for example, proposed by Patent Document 1 (JP-A No. 2006-339089).
Patent Document 1 discloses a technique in which a porous member made from carbon fibers as a base material is molded by a molding jig provided with a plurality of passage molds that are extended into a rectangular parallelepiped shape, by using a paper making method, and after the molding process, by drawing out the molding jig, a gas flow passage is formed inside the gas diffusion layer.